The present invention is directed to a casting, such as a drill bit casting, including in-situ cast inserts and in particular to a casting wherein the insert is partially located within a sleeve member such that the sleeve member insulates the insert from direct contact with the casting material.
Previous attempts to form a casting with bare outwardly projecting in-situ cast tungsten carbide inserts have not been successful. The bare inserts were placed within a mold and a molten metal casting material was cast into the mold such that the casting material was in direct contact with the inserts. The interface between the steel casting material and the inserts was brittle. The inserts that remained intact after the solidification of the casting material shattered upon the application of shot blasting or other mechanical handling. This condition is thought to be due to brittle carbides at the boundaries of the interface between the insert and the casting material. The present invention provides a method for forming a casting having in-situ cast inserts that remain sound, intact and firmly in place through all post-casting processes, such as shot blasting and heat treatment.